1. Field of the Invention
The present invention relates to a polymerized toner used for development in copying machines, facsimile machines, laser printers or the like by electrophotography.
2. Description of the Related Art
Recently, image-forming devices such as copying machines, printers or the like by electrophotography have been of very wide prevalence in offices or the like. Also, meeting the needs of colorization of such a device has been proceeded lately. Particularly, higher resolution and higher printing speed are required for office use, thus, a toner to meet the requirement is needed.
In order to attain higher resolution, a method to obtain a toner having high transferability and high dot reproducibility using a spherical toner (polymerized toner) by various polymerization methods is suggested. Herein, the polymerized toner means a toner for developing an electrostatic latent image produced by various polymerization methods.
Also, in order to achieve higher speed, it is required for a toner to be able to fix at lower fixing temperature (low-temperature fixing ability), thus, various methods are proposed.
Japanese Patent Application Laid-Open (JP-A) No. Hei. 10-282822 discloses an image-forming method using a toner which contains 5 to 40 parts by weight of a low-softening point substance as a release agent of the polymerized toner, has a specific range of physical property of a THF insoluble content of the toner and has a melt index value from 0.5 to 15 g/10 min at 125° C. under load of 49.0 N (5 kgf).
Also, JP-A No. 2001-147550 discloses a toner which contains a multifunctional ester compound, which has 5 or more ester bonds in a molecule, has a molecular weight from 2,000 or more, dissolves to 100 g of styrene by 5 g or more at 35° C., and has an acid value of 2 mgKOH/g or less, as a release agent.
WO1998/20396 corresponding to U.S. Pat. No. 6,132,919 discloses a polymerized toner having a core-shell type structure in which a core particle, comprising a colored polymer particle containing a multifunctional ester compound composed of polyalcohol of trifunctional or more and carboxylic acid as a release agent and a colorant, is covered with a shell layer.
The methods disclosed in the above-mentioned publications improve low-temperature fixing ability in certain degree, however, a new problem is caused wherein a toner easily leaks from a developing cartridge. If the toner leaks, the leaked toner scatters in a developing apparatus leading to problems such as spoiling a printed product, and annoying users with the toner smudging their hands when changing a developing cartridge.